Amelanotic Cellular Blue Nevus

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Abstract
Blue nevus and its variants typically present as pigmented lesions. Dermal melanin is responsible for coloration and is an expected histologic finding. Herein, we report 20 cases of an unusual amelanotic variant of cellular blue nevus . Our series showed clinical demographics similar to pigmented counterparts. Thus, there was a predilection for young individuals with a mean age of 24 years (range 6–74 years). Both sexes were affected, with a female-to-male ratio of approximately 2:1. The lower back, distal extremities, and scalp were the most common sites of occurrence. Importantly, the lack of pigmentation resulted in an atypical clinical appearance. A diagnosis of blue nevus by the attending physician was not considered in any of the reported lesions. All of the tumors extended deep into the reticular dermis or subcutaneous fat with a mean thickness of 5.5 mm (range 1.7–11 mm). Ulceration was present in two lesions. Mild cytologic atypia and pleomorphism were present in five cases. Mitotic activity (up to 3 mitoses/mm2) was observed in 11 lesions. A brisk lymphocytic host response was present in only one lesion. Tumor necrosis was not observed. Most, but not all, tumors showed reactivity for S-100 and HMB-45. Clinical follow-up (mean 32 months) was consistent with a benign course. Local recurrence was not observed after complete excision. None of the cases was associated with clinical evidence of lymph node or distant metastases. Recognition of amelanotic cellular blue nevus is important because the lack of expected pigmentation may result in clinical and pathologic diagnostic difficulty. In particular, amelanotic cellular blue nevus must be distinguished from malignant cellular blue nevus and other variants of melanoma.

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